Gas turbines are widely used in different types of aircraft propulsion engines. In turboprop engines, turbines are used to rotate a propeller that creates the propulsion force. In turbojet engines, turbines are used to produce a jet exhaust that creates the propulsion force. Both turboprop and turbojet engines have advantages and disadvantages. In the past, attempts have been made to combine the advantages of both types of engines. One common result of such a combination is the fan jet engine. In fan jet engines, a turbojet engine is substantially entirely surrounded with a fan air duct. Additional thrust is provided by accelerating the air that passes through the fan air duct. Among the advantages of fan jet engines is their low noise, which results from this bypass and from the shielding effect provided by the fan air duct. Further, the stationary cowls or shrouds that define the outer wall of the fan air duct provide additional turbine blade burst protection. While having these and other advantages, fan jet engines, particularly high bypass ratio turbofan jet engines, have disadvantages. For example, the stationary cowls or shrouds of such engines are difficult to attach both to the engine and to the aircraft to be propelled by the engine.
In addition to fan jet engines, various other attempts have been made to combine the advantages of turbojet and turboprop engines. Mainly, these proposals have suggested adding propeller-type blades to turbojet engines. Proposals have been made to add propeller blades to the front, the rear and the mid regions of turbojet engines, see for example U.S. Pat. Nos. 2,478,260, 2,404,768 and 3,811,791. For various reasons, these proposals have not been adopted or, if adopted, have not been widely used.
The present invention is directed to providing a hoop fan jet engine that combines the advantages of turbojet and turboprop engines.